Olfactory receptors are nothing to sniff at
Proteins essential to smelling are found throughout the body – but their function remains mysterious. Andrew Masterson reports.
Proteins in the nose that bind to odorants, facilitating the sense of smell, are also found in many other parts of the body, and research is revealing that they have a wide range of critical functions unrelated to distinguishing between a rose and a chicken curry.
In recent years, the proteins, known as olfactory receptors (OR), have been discovered in many organs, including lungs, intestines, liver, heart and blood, but their function has been largely unknown.
In a paper published in the journal Physiological Reviews, cell physiologists Désirée Maßberg and Hanns Hatt from Ruhr-University Bochum in Germany comb through more than 200 studies in which ORs are identified, in an attempt to better identify their functions.
The results are potentially extraordinary.
The researchers found that olfactory receptors located in heart muscle cells may play a role in regulating heart function, while others located in the immune system may be linked to the death of some types of leukaemia cells.
In a similar manner, ORs present in the liver and the colon may put the brake on cancer cell proliferation. They may also have a similar function in the prostate, especially among men with prostate cancer, although the evidence is unclear concerning whether in this circumstance they restrict or promote tumour cell growth.
One thing, however, seems abundantly clear. Olfactory receptors are involved in a lot more than just smelling.
“Considering that ORs occur in nearly the entire human body, they appear to be substantially more functionally important than previously suggested,” the authors write.
“In the last decade, an increasing number of studies have shown their ability to operate in physiological and pathophysiological cell processes.”
The implications for further research are obvious. However, Maßberg and Hatt note that analysing the exact functions of ORs outside of their olfactory roles “remains a major challenge”. So far, they say, the specific effects of less than 10% of non-nasal OR’s have been identified.
“The extranasal expression of ORs is a new and exciting area of science that should attract young scientists because of the exciting recent breakthrough discoveries,” they conclude.